How Do Wheat Herbicides Affect Fall Cover Crops?

01/09/17

Here’s a new perspective on cover crops for the New Year.

Wheat offers the best opportunity for North Dakota producers to plant cover crops, with a large diversity of species options. One problem that occurs is that many common wheat herbicides have crop rotation restrictions of 4-18 months to many crops. How safe is it to plant a cover crop in that case? Herbicide labels do not have enough information to confidently make cover cropping decisions. In 2016 a study was conducted to answer this question at three locations in North Dakota. Nine herbicides were used which have the potential to still have a residual around 60 days after application. A diversity of active ingredients was chosen. Cover crop injury was grouped by risk. For cover crops we are assuming that most people would be comfortable with 20% or less injury to the crop so we call this ‘low risk’ (LR), which is our safest rating. If any herbicide caused 21-50% damage we are calling it ‘medium risk’ (MR) to the cover crop. If there was over 50% damage, the herbicide and cover crop combination was deemed ‘high risk’ (HR). The word risk is used since one of the locations saw no injury from any of the herbicides. To account for this, I took a conservative approach and summarized the data based on the highest amount of damage recorded at any location. The Carrington location saw the most damage, followed by Hettinger with only marginal cover crop injury, followed by Fargo with no injury. Injury levels will vary based on organic matter, soil texture, rainfall (and soil moisture), and temperature. Seed for this study was donated by Pulse USA.

Risk of cover crop injury based on highest damage recorded between Carrington, Fargo, and Hettinger, ND